Porphyrin-cellulose nanocrystals: a photobactericidal material that exhibits broad spectrum antimicrobial activity.

Towards our overall objectives of developing potent antimicrobial materials to combat the escalating threat to human health posed by the transmission of surface-adhering pathogenic bacteria, we have investigated the photobactericidal activity of cellulose nanocrystals that have been modified with a porphyrin-derived photosensitizer (PS). The ability of these previously synthesized porphyrin-cellulose-nanocrystals (CNC-Por (1)) to mediate bacterial photodynamic inactivation was investigated as a function of bacterial strain, incubation time and illumination time. Despite forming an insoluble suspension, CNC-Por (1) showed excellent efficacy toward the photodynamic inactivation of Acinetobacter baumannii, multidrug-resistant Acinetobacter baumannii (MDRAB) and methicillin-resistant Staphylococcus aureus (MRSA), with the best results achieving 5-6 log units reduction in colony forming units (CFUs) upon illumination with visible light (400-700 nm; 118 J cm(-2)). CNC-Por (1) mediated the inactivation of Pseudomonas aeruginosa, although at reduced activity (2-3 log units reduction). Confocal laser scanning microscopy of CNC-Por (1) after incubation with A. baumannii or S. aureus suggested a lack of internalization of the PS. Research into alternative materials such as CNC-Por (1) may lead to their application in hospitals and healthcare-related industries wherein novel materials with the capability of reducing the rates of transmission of a wide range of bacteria, particularly antibiotic resistant strains, are desired.